This invention relates to a brake fluid pressure control apparatus in an anti-lock control system for a vehicle, equipped with a mechanism for relieving a kickback which acts on a brake pedal during anti lock control.
A phenomenon called "kickback" has been known to occur during anti lock control by an anti-lock control system which serves to monitor and assess a wheel skid condition of a vehicle, and to increase or to decrease a brake fluid pressure applied to wheel cylinders or to hold the fluid pressure at a constant value. This kickback phenomenon occurs when a control signal causes a great volume of return-pressure fluid to flow from the wheel cylinders to a reservoir, thereby being returned to a pressure fluid supply passage which communicates a master cylinder with a pressure control valve. When this great volume of return-pressure-fluid acts on a pressure generating chamber of the master cylinder, the brake pedal is pushed back rapidly and strongly, thereby causing a driver to experience a disturbing or uncomfortable feeling.
U.S. Pat. No. 4,453,782, for example, discloses a fluid pressure control apparatus for an anti-lock control system that was conceived for the purpose of eliminating the above-mentioned kickback phenomenon. This fluid pressure control apparatus is equipped with a valve device (gate valve) which allows the pressure fluid from the master cylinder to be communicated with the pressure control valve when the fluid pressure exceeds a certain value. A discharge outlet of a hydraulic pump is connected to the pressure fluid supply passage between the valve device and the pressure control valve.
Since in this fluid pressure control apparatus the valve device hinders the flow of the return-pressure-fluid from the wheel cylinders into the master cylinder, a pressure accumulator for this return-pressure-fluid must be provided. However, the adding of the accumulator and the valve device at the discharge side of the hydraulic pump results in rather large-sized in the anti-lock control system.
Moreover, as the "kickback" does not occur in said apparatus, a driver does not realize that he is in a condition of anti-lock control.